The invention relates in general to gun-launched projectiles and in particular to apparatus and methods for obtaining consistent gun chamber pressure for gun-launched projectiles.
It is known that the chamber pressure in a gun directly affects the velocity of a projectile. An accurate and consistent velocity requires an accurate and consistent chamber pressure. Some known methods for obtaining consistent chamber pressures include shot start rods and crimping.
A shot start rod connects the cartridge case to the projectile with grooves that are designed to break at a desired pressure. The shot start rod is secured lengthwise between the cartridge case and the projectile with a necked down section in the rod body. When the cartridge is ignited, the necked down section of the rod will fail at a desired chamber pressure. Until the desired pressure is reached, the rod holds the projectile in place in the gun tube. After the desired chamber pressure is reached, the rod will break and the projectile will follow a normal interior projectile travel. A shot start rod adds weight to a weapon and decreases the size of the usable space in a weapon's chamber.
Crimping is common in larger ammunition and works by bending or crimping the outside shell of a cartridge case to the grooves on the projectile. Crimping has been used in 105 mm rounds. As with the shot start rod, the crimp holds the projectile in place until the desired chamber pressure is reached. At that point, the crimp fails and the projectile is released. The chamber pressures achieved with crimping can be inconsistent and difficult to quantify.
The lethality of a projectile is directly related to its velocity and its velocity is directly related to the gun chamber pressure. A need exists for an apparatus and method for obtaining accurate and consistent chamber pressure in a gun tube.